The noise in my motor is too loud

It has come to the point that I can no longer ignore how much more noise I hear from my M20 motor. After 243,000 miles, I think it must be time to take it apart and put some new bearings in it. My concern is that just bearings will do the job. The noise goes away after a minute or so of running. So maybe my crank is still ok.

Anyone have advice of what to look for when it comes apart to explain the noise and assure that I have guessed correctly about the cure?

Yes a complete rebuild is probably what it needs. I plan to replace all the bearings and piston rings. Hope the pistons can be re used.
The fluids are all drained today and most wires and tubes disconnected. I hope I can remember where they all go when it comes time to connect them all.

QuoteBob in Everett
Yes a complete rebuild is probably what it needs. I plan to replace all the bearings and piston rings. Hope the pistons can be re used.
The fluids are all drained today and most wires and tubes disconnected. I hope I can remember where they all go when it comes time to connect them all.

QuoteBob in Everett
Yes a complete rebuild is probably what it needs. I plan to replace all the bearings and piston rings. Hope the pistons can be re used.
The fluids are all drained today and most wires and tubes disconnected. I hope I can remember where they all go when it comes time to connect them all.

That is what the mobile phone is for. Take pictures before removal.

Like Ove said, make pictures. Lots of pictures. Then post some here!
...You can use adesive tape or masking tape to label the plugs and tubes, and you will be glad you did so when the time comes to put it all back together.
Also the small bolts and bits, keep them in order wraped in a sheet of paper and marked where they belong. Soon you will have a bunch of bits all mixed up and waste a lot of time looking wich goes where.

Have been tempted to modifications for increased power but have resisted so far. Planning only piston rings and bearings. Hopefully will not have to have the crankshaft worked on. I sure enjoy driving this car and hope to drive it until I cannot drive any more.

QuoteBob in Everett
Have been tempted to modifications for increased power but have resisted so far. Planning only piston rings and bearings. Hopefully will not have to have the crankshaft worked on. I sure enjoy driving this car and hope to drive it until I cannot drive any more.

More power is not always a good thing. You may tune the engine to better economy or smooth operation.

QuoteBob in Everett
It has come to the point that I can no longer ignore how much more noise I hear from my M20 motor. After 243,000 miles, I think it must be time to take it apart and put some new bearings in it. My concern is that just bearings will do the job. The noise goes away after a minute or so of running. So maybe my crank is still ok.

Anyone have advice of what to look for when it comes apart to explain the noise and assure that I have guessed correctly about the cure?

Hey Bob

Have you done a compression test on this motor lately? My 1988 325is has 225k and still pulls factory compression figures....

If the motor was making noise, any idea where from?

It's always nice to take a few readings before the engine comes apart and then a few mid tear down, like end float on the crank and piston to wall clearences. I've been at this many times and am glad to help.

Rick,
I changed the head due to a cracked original about 18 months ago. There was some coolant leaking into the crankcase. The replacement head gave me 180 psi on compression test after it was all back together. I had notice a knocking noise on cold starts for some time. It was quiet for about 5 seconds and then gradually got louder for a couple of minutes before quiet again. When warmed up and running, no noise. Of late the noise on cold start has gotten louder and lasting longer.

I just hope the crank is not damaged. The coolant in the oil last year probably did not help. The engine has 243,000 miles on it so it might be due but has been driven reaonably and not revved up to the high end much at all.

QuoteBob in Everett
Rick,
I changed the head due to a cracked original about 18 months ago. There was some coolant leaking into the crankcase. The replacement head gave me 180 psi on compression test after it was all back together. I had notice a knocking noise on cold starts for some time. It was quiet for about 5 seconds and then gradually got louder for a couple of minutes before quiet again. When warmed up and running, no noise. Of late the noise on cold start has gotten louder and lasting longer.

I just hope the crank is not damaged. The coolant in the oil last year probably did not help. The engine has 243,000 miles on it so it might be due but has been driven reaonably and not revved up to the high end much at all.

Well, at that mileage you where probably hearing some piston slap but not having heard it .....?

The motor was leaking oil from the head gasket so much it was difficult to tell if it was burning any oil. The gasket I had put on last did not have any sealant around the edges like the one before that which did not leak. Did not do a compression check prior to disassembly but it ran fine once it got warmed up. The knocking noise sounded like a connecting rod bearing. Once it was apart, I could not see any obvious damage that would explain the noise. I need to make some measurements of the journals to see if I can find any flat spots.

I am surprised to see quite heavy deposits on the pistons. I have not take a road trip in several weeks so it has just been city driving and winter. Probably should use a wire wheel to brush off the deposits.

QuoteBob in Everett
The motor was leaking oil from the head gasket so much it was difficult to tell if it was burning any oil. The gasket I had put on last did not have any sealant around the edges like the one before that which did not leak. Did not do a compression check prior to disassembly but it ran fine once it got warmed up. The knocking noise sounded like a connecting rod bearing. Once it was apart, I could not see any obvious damage that would explain the noise. I need to make some measurements of the journals to see if I can find any flat spots.

I am surprised to see quite heavy deposits on the pistons. I have not take a road trip in several weeks so it has just been city driving and winter. Probably should use a wire wheel to brush off the deposits.

Careful with the wire wheel Bob, those things can do a lot of damage. Do the cleaning with a hand tool, it takes longer but you won't hurt anything. If it was a bottom end making noise the oil light should have been flickering at idle when hot. You can do a good visual of the pistons and walls and then start measuring. Don't forget to do the end float on the crank before you take anything down. It's an easy test that will tell you a lot.

End float was pretty tight. I could not really get enough movement to tell that it was moving. Probably should have use a feeler gage. So far have not found enough damage to say what the cause was. I never get oil light flicker no matter how hot the engine is. I run 20-50 oil. wanted to check the oil pressure with a gage but the pressure switch does not have the type threads I can adapt anything I have to fit.

The carbon build up on the piston heads is probaby a 1/16 inch thick in places. I always buy my gas at Costco because it is close and less expensive than elsewhere. Maybe I should be buying some Shell or something.

QuoteBob in Everett
End float was pretty tight. I could not really get enough movement to tell that it was moving. Probably should have use a feeler gage. So far have not found enough damage to say what the cause was. I never get oil light flicker no matter how hot the engine is. I run 20-50 oil. wanted to check the oil pressure with a gage but the pressure switch does not have the type threads I can adapt anything I have to fit.

The carbon build up on the piston heads is probaby a 1/16 inch thick in places. I always buy my gas at Costco because it is close and less expensive than elsewhere. Maybe I should be buying some Shell or something.

Bob

You can measure end float with a feeler but a dial indicator is really the only way to go. The carbon build up can loosened up with solvent and gently scraped off, you'll want to slide a feeler gauge between a clean piston and it's wall in several places to see what your clearances are.

The carbon build up on the piston heads is probaby a 1/16 inch thick in places. I always buy my gas at Costco because it is close and less expensive than elsewhere. Maybe I should be buying some Shell or something.

Bob

For a few years in the '80s I would only buy Amoco gas because I thought it was going to keep my engine clean. When I finally rebuilt that engine, I found it had the worst build up of any engine I had seen the insides of up to then. It was awful, huge deposits on the intake valves, thick carbon all over the pistons, what a mess. Since then I've just bought whatever was cheap and convenient for fuel, and the insides of the engnes I have opened up have looked better. It might just be that variety is a good thing.

I have the pistons out already so can measure them direcly. The cylinders have only the slightest wear ridge showing. They slid out easily. Hone marks are still lightly evident on the cylinder walls.
I am studying the oil galleries to see if I can determine why one connecting rod my not be getting proper oil. There are a lot of deep drilled holes that must intersect to form them .

QuoteBob in Everett
Here are a few pictures of the disassembly. The wear scar on the #1 piston measures the correct diameter but the measurement at 90deg to the scar is 0.015 inches smaller. Seems veery odd.

Looks like you're marking everything, thats a good idea. Often rod/main caps are not marked so it's best to do it as the tear down goes forward. It's too bad you did not do an oil presure test (static) to see if you had any leaks in the oiling system, that would have ttold you if and where your oiling problems are.

Did you see any bad areas on the rod/main bearings or the crank journals?

You said something about the walls having a small ridge on the top. It's always amazing to me how this German metal wears; not just hard but.... I guess the best word I can come up with is annealed. When metal becomes forgiving and tough. The metal is sort of magical compared to other car makers stuff....

One rod journal had a larger clearance than the others. But only 0.0039 instead of 0.0018. Doesn't sound like much but maybe it is enough. One piston has a worse wear scar than the others but all measure within tolerance allowed.

The info in Bentley about the crank says it is heat treated by BMW and should not be ground unless it can be re heat treated. I suspect it could be ion nitrided. That is a very good hard coating that is very thin. The cylinder walls are cast iron which can be treated with a steam treatment of some kind to make it very low friction and wear resistant. Might be something like that.

QuoteBob in Everett
One rod journal had a larger clearance than the others. But only 0.0039 instead of 0.0018. Doesn't sound like much but maybe it is enough. One piston has a worse wear scar than the others but all measure within tolerance allowed.

The info in Bentley about the crank says it is heat treated by BMW and should not be ground unless it can be re heat treated. I suspect it could be ion nitrided. That is a very good hard coating that is very thin. The cylinder walls are cast iron which can be treated with a steam treatment of some kind to make it very low friction and wear resistant. Might be something like that.

The noise you were hearing Bob, was it a bottom end noise. You know, crankshaft speed? deep thuding type noise/rumble/knock?

QuoteBob in Everett
One rod journal had a larger clearance than the others. But only 0.0039 instead of 0.0018. Doesn't sound like much but maybe it is enough. One piston has a worse wear scar than the others but all measure within tolerance allowed.

The info in Bentley about the crank says it is heat treated by BMW and should not be ground unless it can be re heat treated. I suspect it could be ion nitrided. That is a very good hard coating that is very thin. The cylinder walls are cast iron which can be treated with a steam treatment of some kind to make it very low friction and wear resistant. Might be something like that.

So, you've got one rod journal with almost 4 thousands under. That sounds a little wide to me Bob. What does the book say for alowable clearence?

The noise was a deep sound like the lower end. Only once every other rev I estimated. When first starting the engine, it would be quiet for about 3-4 seconds and then gradually get louder for a few seconds and stay that way for a couple minutes then slowly get quiet. Once warmed up the engine did not make the perceptable noise.

The stock clearance is about 0.0018 and one journal had 0.0039 clearance. The crank journals all measured within tolerance and appeared to be round. I could not detect any out of round. The one rod bearing ID had what appeared to be a bit more wear than the others with a spot that appeared to have worn through the babbit material. That is the one that is 0.0039 clearance to the crank. Some of the pistons have wear marks on the skirt on one side but they still measure within tolerance to that diameter. What I found odd was that all the pistons appear to be oval. On the axis parallel to the wrist pin, the OD is about 0.015 less than perpendicular to the pin.

Oval pistons may be normal, they are supposed to be round when hot.
If you have the chance to compare to known good parts, it would be nice.
I hope you have all those psecs from the manual, the Bentley or the Haynes...

Yes, I have been using the Bentley manual for specifications. The top of the pistons appears to be round and larger than the skirt sides perpendicular to the wrist pin. The large diameter skirt matches the diameter shown in the Bentley. All of which means that none of the pistons meets the ovality requirement. Not sure what it means though. Should they be replaced or just use new rings and move along.

Pistons are not supposed to be oval, they just get that way from wear Jose. The piston slap you hear on old motors is oval pistons in worn holes not warmed up yet... needing to get rounder from heating up.

Bob, if the pistons are beyond spec it's time for a rebore and new pistons but with that one shy journal on the crank it might be time for a rethink. Putting new pistons in old holes is not a sound idea.

Really I do agree with you that new ones might be best but the cost of standard size pistons seems pretty high. I decided to go back with the same old pistons but had a set back today. The last piston was just about all the way in and the middle ring came out of the compressor and broke the edge of it. So I have to order up a new set of rings for that piston.
New pistons would have doubled the cost of my "overhaul" while a set of oversize pistons would have been less, I would then have to return all the bearings and rings then machine the block.

The piston bores all had a very low amount of wear and the hone marks were still visible in all the cylinders.

Made a few more checks during assembly. The rings have the maximum end gap due to cylinder wear probably. If I have to do the engine over again it will mean a bore and oversize pistons. Hope I can get a few more years out of this rebuild.

The engine is going back to gether well enough. Head is on and timing belt. Now to hang it on the hoist so can put the new clutch on. Have to put new seals in the trans before mating it to the engine.
It will be really nice to not have oil leaks for a change. Already looking forward to getting on the road again.

QuoteBob in Everett
Made a few more checks during assembly. The rings have the maximum end gap due to cylinder wear probably. If I have to do the engine over again it will mean a bore and oversize pistons. Hope I can get a few more years out of this rebuild.

The engine is going back to gether well enough. Head is on and timing belt. Now to hang it on the hoist so can put the new clutch on. Have to put new seals in the trans before mating it to the engine.
It will be really nice to not have oil leaks for a change. Already looking forward to getting on the road again.

All sounds good Bob, did you think to plastigage the big ends of the rods, or at least that bad journal you had?

The only thing to consider in putting new rings in an old clylinder is it may cause the top ring to break from the ridge of the top of the cylinder.

Hopefully you did not have a noticable one so you might be fine. They're very easy to feel for with your finger nail....

I did not do plastigage. I measured the crank journals pretty carefully. They were all withing limits and did not appear to have any flat spots. The cylinder ridges were barel perceptable. There were still some hone marks in all the cylinders.

The engine is assembled and setting in the car. almost all hooked up excpet for coolant. Oh, and the drive shaft and exhaust is still laying beside the car. The drive shaft center support bearing seems like it is pretty difficult to change. There must be a trick to it.